PALEOMAGNETIC STUDY OF TRIASSIC SEDIMENTS FROM THE SILICA NAPPE IN THE SLOVAK KARST, A NEW APPROACH

Abstract: Intensive paleomagnetic and rock magnetic study were performed for Triassic limestones from the Silica Nappe in the Slovak Karst. Five exposures situated on the eastern and western side of the Stitnik - Plesivec fault were sampled for this study. In all exposures a secondary component of remanence of normal polarity (N), carried by secondary PSD magnetite was found. In the Silicka Brezova exposure (SB) apart from the N component, another secondary component of reversed polarity (R), carried by hematite, was isolated. Both components were acquired after folding. The R component was acquired during the Odra reversal event in the Oligocene (Birkenmajer et al. 1977). Comparison of its direction with the reference data let us conclude that the area belonged during this time to the African affinity. The declination of the R component suggests that after this magnetization period the studied region rotated anticlockwise by about 90° around an intraplate vertical axis together with the whole Pelso megaunit. According to Marton et al. (1995) and Marton & Fodor (1995) the rotation took place in two phases, the first one by about 50° took place in the Early Miocene, the second one, by about 30° - in the Late Miocene. The N component, isolated by us, seems to have been acquired during the Middle Miocene after the first and before the second. rotational phases: its declination agrees with a counterclockwise rotation of the Nappe by about 30–40° during the Late Miocene, as postulated by the cited authors. The inclination of the N component is lower, than the expected for Miocene, but agrees with the Miocene results for the Bukk region also belonging to the Pelso block, confirming the idea about the Miocene „southern escape“ of the Pelso bloc (Marton 1993). The final tectonic activity in the study area was connected with formation of the Stitnik-Plesivec fault (Late Tertiary - Quaternary). Our results suggest, that the fault is of rotational type and resulted in different tilting of beds situated on its eastern and western sides.